1. Field of the Invention
The present invention relates to a cooling apparatus, particularly a cooling apparatus having an improved cooling vessel. The cooling apparatus is used for an air-conditioning apparatus for automobiles, vessels, or residences, or in cooling apparatus of shipping containers for food products or medical products that require refrigeration.
2. Description of the Prior Art
Prior known cooling apparatuses for air-conditioning or refrigeration include a well-known heat pump system and, more recently, an adsorption system that uses adsorbents such as zeolite.
The prior technology is exemplified by what is described in Japanese Laid-Open Patent Application 61-139098, filed Jun. 14, 1986, Laid-Open No. 62-5060, laid-open Jan. 12, 1987, priority being claimed on German Patent Application P3521484.8, filed Jun. 14, 1985.
The present applicant has disclosed in a copending U.S. application Ser. No. 08/066,984 filed May 25, 1993, an improved adsorption-type cooling system.
FIG. 20(a) and FIG. 20(b) illustrate a basic principle of a prior known single-adsorber type adsorption cooling system. In FIG. 20(a), an adsorber 1 is connected with a cooling vessel 2 by a tubular passage 4 having a shutoff valve 3. The adsorber 1 houses adsorbent 1a such as zeolite, and a heat exchange pipe 5 that is in contact with the adsorbent 1a. The cooling vessel 2 contains water as an adsorption medium (adsorbate) which is in thermal contact with a cooling pipe 6. The air which is to be cooled is circulated through the cooling pipe 6. The adsorber 1, the cooling vessel 2 and the tubular passage 4 constitute a closed system which is evacuated of air. A condenser 7 for exchanging heat with the ambient air is provided on the tubular passage 4 near the cooling vessel 2.
With this cooling system, when the valve 3 is opened, the water inside the cooling vessel 2 evaporates into water vapor and flows through the tubular passage 4, in the direction shown by the arrow, into the adsorber 1 to be adsorbed by the adsorbent 1a by its adsorption action. Because of this, when the water in the cooling vessel 2 evaporates, the latent heat is adsorbed in the cooling vessel 2, so that the temperature in the cooling vessel 2 declines so as to cool the air inside the cooling pipe 6. This operation is called an adsorption process.
Next, an explanation will be made on the operation whereby the water adsorbed by the adsorbent 1a is returned to the cooling vessel 2.
Referring to FIG. 20(b), a high temperature gas from an external heat source is provided through the heat exchange pipe 5 to heat the adsorbent 1a and thereby desorb and separate the water adsorbed in it. Then, the separated water in a state of vapor is driven through the tubular passage 4, in the direction shown by the arrow, to the condenser 7, where the water vapor becomes liquid water and is recovered in the cooling vessel 2. This operation is called a desorption process.
The adsorption here means a state where the water molecules are retained among the molecules of the adsorbent. Reversely, in the desorption action, the water molecules are desorbed and separated from the molecules of the adsorbent as the adsorbent is heated.
However, the single-adsorber type adsorption cooling system described above is incapable of continuous cooling because the adsorption process and the desorption process must be done alternately in the same system. With this in mind, a dual-adsorber type adsorption cooling system as shown in FIG. 16 has been proposed.
In FIG. 21, two adsorbers 8, 9 are individually connected to a single cooling vessel 14 by tubes 12, 13, which respectively have shutoff valves 10, 11. The water in the cooling vessel 14 is thermally contacted by a cooling pipe 15 in the same manner as in the case of the single-adsorber type adsorption cooling system described above. Adsorbents 8a, 9a in the adsorbers 8, 9 are also in thermal contact with heat exchange pipes 16, 17, respectively, and condensers 18, 19 are provided on the tubes 12, 13, respectively.
With this cooling system, while the adsorption process is performed at one adsorber, at, for example, the adsorber 8, the desorption process is simultaneously performed at the other adsorber 9. Then, the two adsorbers 8, 9 carry out a switching operation whereby they work in reverse when their respective processes have been completed. Since the adsorber 9 is at high temperature when the desorption operation has been completed, low or ambient temperature air is provided through the heat exchange pipe 17 to cool the adsorbent 9a. Continuous cooling in the cooling vessel 14 is thus made possible by periodically repeating such operation.
(Problems to be Resolved)
With an adsorption type cooling system as described above, when the operation of the cooling system is temporarily suspended the cooling action in the cooling vessel by the evaporation of the water will be stopped. And the temperature of the water in the cooling vessel will rise if the operation is suspended for a while. This will result in an ineffective cooling when the system resumes operation. By increasing the quantity of the water in the cooling vessel, the thermal capacity retained by the cooling vessel will be increased. However, the greater thermal capacity is translated to a longer rise time at the first operation of the cooling apparatus and an increase of its size.
In order to increase the cooling effect, the evaporation rate of the water must also be increased. However, increasing the surface area of the water to obtain an increased rate of evaporation will result in an increase in the size of the cooling vessel.